I have a 2007 Chevy Uplander LS and when I turn the key, nothing happens. No dash lights come on, no radio, no lights, no power, no crank, no sounds. I thought it was the battery because the battery was dead, so I replaced and got a new battery. But still, nothing happens. I cleaned the connections on the battery and the cables. The cables are not corroded and in good shape. I also recently replaced the starter and the alternator as well. So why won't it start?

 

that sounds like relays and fuses issues if not that look for loose connections or computer system problems

 

Maybe an ignition lock that gone bad? Can you start the radio or turn the light on? If not, a main fuse like Carl suggested.